15. Read the text to get the gist of it. Answer the following question.
What are the types of weirs?
Text B Measurement of Flow in Open Channels
The flow in large natural channels is usually measured with some types of meters. The flow in small streams and man-made channels may be more conveniently measured by other methods. Among the most common methods are the use of weirs and venturi-type flumes.
Weirs are the following: sharp-crested rectangular weirs, triangular or V-notch weirs and trapezoidal weirs. For weir to give accurate water discharge, the upstream face of the weir must be vertical and at right angles to the channel, and the crest of the weir must be horizontal. In addition atmospheric pressure should be maintained under the nappe, and the approach channel should be straight and without any obstruction. Corrosion of the weir crest or damage by floating debris may alter the weir coefficient.
When the water level downstream from a weir rises above the level of the weir crest, the weir crest is said to be submerged and under such conditions accurate flow measurement is not possible because surface disturbances of water downstream from the weir make it difficult to measure the depth of submergence.
The head on a weir is usually measured with a staff gage, though better results are obtainable with a hook or point gage in a stilling well. Inaccurate head determination will provide sizable error in measurements.
If water contains suspended particles, some of them will be deposited in the pool located above a weir, resulting in a gradual change in the weir coefficient. Moreover, the use of a weir results in a relatively large head loss. Both these difficulties are at least partially overcome by use of venturi-type flumes. For obtaining best results venture-flumes ought to be installed in a straight section of channel where flow conditions are relatively uniform. Usually venturi-flumes are made of galvanized iron, plain and reinforced concrete.
16. Finish the following sentences according to the text.
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The flow in large natural channels is usually measured with …
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Among the most common methods are the uses of …
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The upstream face of the weir must be vertical and …
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Atmospheric pressure should be maintained under …
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The approach channel should be straight and without …
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Corrosion of the weir crest or damage by floating debris may alter …
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The head on a weir is usually measured with …
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The deposition of suspended particles results in …
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Venture-flumes ought to be installed in …
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Venturi-flumes are made of …
17. Answer the following questions.
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What meters are used to measure the flow in open channels?
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What are the types of weirs?
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What is necessary for weirs to give accurate water discharge?
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What may alter the weir coefficient?
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Is accurate flow measurement possible?
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What is the head on the weir usually measured with?
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What provides sizable error in measurements?
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What happens if water contains suspended particles?
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What difficulties are partially overcome by use of venture-type flumes?
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Where must venture-flumes be installed for obtaining the best results?
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What are venture-flumes made of?
18. Make a short summary of the text.
19. Find the synonyms of the following words in the text.
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1. to change - … |
5. permanent - … |
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2. to form a sediment - … |
6. blocking - … |
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3. to immerse - … |
7. exact - … |
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4. coefficient - … |
8. to set down - … |
20. Find the opposites of the following words in the text.
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1. upstream - … |
5. vertical - … |
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2. natural - … |
6. accurate - … |
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3. restricted - … |
7. worst - … |
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4. variable - … |
8. sharp - … |
21. Fill in the correct prepositions where necessary then choose any three items and make sentences.
1) to result ___ sth.; 2) to be ___ right angle; 3)___ addition; 4) to measure ___ sth. ___ sth; 5) to be made ___ iron; 6) to be installed ___ the straight section; 7) to provide ___ an error ___ measurements.
22. Translate the following words into English using the vocabulary of the text.
Измерительный прибор, использовать треугольный водослив Томсона, водослив с острым прямоугольным гребнем, трубка Вентури, поддерживать напор воды, прямой подводящий канал, неизменные условия, изменять коэффициент водослива, измерять при помощи водомерной рейки в водобойном колодце, потеря давления, неточное определение напора, частично преодолевать, атмосферное давление.
23. Find the translation of the following terms and memorize their meaning.
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scarce |
dynamic energy |
to preclude |
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public water supplies |
elastic energy |
sewers |
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opportunity |
back and forth |
rarely |
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pollution |
to damp out |
principal |
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internal pressures |
friction |
direction |
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external pressures |
surge tanks |
interconnections |
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static pressure |
air chambers |
to satisfy |
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check valves |
asphaltic fiber |
liquid |
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blow off valves |
asbestos-cement |
water hammer |
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pressure-relief valves |
vitrified clay |
predetermined |
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abruptly |
copper |
standpipe |
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pure water |
wrought iron |
solids |
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polluted water system |
inverted siphon |
to convert |
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electric heating units |
sag pipe |
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portable water system |
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